1. Field of the Invention
A method and apparatus for correcting surface errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts having piano, concave, convex, spherical, and other complex surfaces.
2. Description of Related Art
Currently, many optical lenses are made beginning with a “blank” starting part (such blank part being an approximately formed and generally roughly finished piece) in several processing steps. The process steps typically include fine grinding, followed by conventional polishing techniques wherein the surface roughness and surface accuracy of the lens is significantly improved. This prior art process is sufficient for many conventional low-precision lenses. However, when the desired lens has a shape that is not spherical or piano and/or where such conventional methodologies cannot be applied (e.g. to aspherics), or where the lens has very high accuracy requirements, such prior art process is not sufficient. In such circumstances, the method and apparatus of the present invention is advantageous.
Heretofore, a number of patents and publications have disclosed methods, apparatus, and compositions for polishing of precision surfaces. United States Patent Application Publication No. US 2004/0229553 A1 of Bechtold et al., which is assigned to the assignee of the present invention and incorporated herein by reference, describes a tool, apparatus, and method for polishing objects. The tool has a rotatable drive wheel engaged with a polishing wheel by use of a polishing foil formed as a flexible belt. The polishing wheel may have a cavity within, the cavity being inflatable using a variety of fluids having a range of physical properties. The polishing wheel is adjustably positionable against an object to be polished by actuating means joined thereto. The apparatus comprises a multi-axis computer controlled machine to which the tool is attached.
In some circumstances, is preferable to configure such an apparatus with a large diameter drive pulley, relative to the polishing wheel. This provides a large length of wrap of the polishing belt around the drive pulley so that it does not slip, and it also provides a high belt speed at a relatively low drive pulley rotational speed. However, if one configures the tool and apparatus of the published application of Bechtold et al. with a large driven pulley and a small polishing wheel, it is less capable of polishing deeply concave surfaces. This is because the angle formed by the straight lengths of belt between the drive pulley and the polishing wheel is large, and may even exceed 90 degrees. Thus the polishing wheel and abrasive belt can not be located within an object with a deeply concave surface, since the belt will rub on the edges of the object before the polishing wheel reaches the concave surface.